When planting corn or other crops, a key decision is the spacing between each seed. Decreasing spacing increases the overall population (i.e., the number of seeds per acre), which increases the number of crop plants in a given area but causes the plants to increasingly compete for sunlight and soil resources, reducing the productivity per plant.
Modern planters such as that disclosed in U.S. Pat. No. 5,956,255 are able to vary the population while planting and to use a “prescription map” prescribing a population (and thus seed spacing) for each location in the field. In planters like that disclosed in the '255 patent, an electronic planter monitor receives the planter's current location in the field from a GPS receiver and consults the prescription map to determine the currently desired population while planting.
When creating a prescription map to optimize yield, it is desirable to set different populations for different soil types and conditions. For example, the optimal population is likely higher with more productive soils. Thus in many cases it is desirable to increase the population when planting in more productive soils and decrease the population when planting in less productive soils.
In order to identify soil types and productivity in a given field, services such as the Soil Data Mart maintained by the United States Department of Agriculture (“USDA”) provide soil data maps such as soil type maps. The soil data maps comprise sets of polygons, each of which constitutes the border around each differentiated soil type or condition. The vertices of the polygons correspond to a latitude and longitude. Each polygon is associated with a data set, which may include the soil type and the estimated yield for various crops.
In FIG. 9A, a tractor 920 is schematically illustrated drawing a variable rate application implement 926 (e.g., a planter) through a field along a direction of travel indicated by an arrow 928. A soil map 900 comprises a polygon 902 having soil type 2, with the area outside polygon 902 having soil type 1. The soil map 900 may be converted to a prescription map requiring a seed population 2 inside the polygon 902 and a seed population 1 outside the polygon 902. As the planter 926 moves across the field as shown in FIG. 9A, it will plant at population 1 until crossing the boundary into polygon 902, at which point it plants at population 2 until exiting polygon 902. Since the planter 926 generally includes multiple row units arranged transverse to the direction of travel, the row units are preferably controlled separately such that, e.g., if the rightmost row unit enters polygon 902 before the leftmost row unit, the rightmost row unit will begin planting at population 2 first. As illustrated in FIG. 9B, the prescription map may also be converted to a raster image 950 instructing the planter to plant at certain populations in discrete areas or “rasters” of the same size.
Several commercially available software programs assist the user in creating planting prescription maps using soil maps and other field data maps. For example, using one commercially available farm management program, the user obtains an image file containing relevant aerial or satellite imagery and obtains a “shape file” comprising soil polygons for a geographical subdivision (e.g., a county) of interest from a soil data server. Typical soil data servers will place the user's soil map requests in a queue; when the user's request is reached, the soil data server searches for the requested boundary, creates a corresponding shape file and alerts the user that the shape file download is available. Once the user has obtained the soil map and aerial imagery, such programs display both images side by side and allows the user to select corresponding points comprising a field boundary on both images. The program then uses the corresponding points to “clip” the polygons in the soil map to the field boundary and displays the clipped soil map laid over the aerial image. Some farm management software programs additionally allow the user to import a field boundary driven and recorded using a global positioning receiver. Once transferred to the software, the GPS boundary may be used to clip aerial imagery to the field boundary.
Commercially available systems described require multiple complex steps to appropriately match field boundaries, aerial imagery and soil data imagery. Such systems also require a dedicated software program on the user's computer to perform the various operations involved. Due to these inconveniences many users choose to employ an agronomy service to generate prescriptions. Thus there is a need for a simpler, faster and more intuitive method of generating prescription maps.